Bring a large pot of salted water to a full boil. Cook corn for 4 minutes, until the starch is cooked off but the corn is still a bit crisp. Drain corn and immediately place corn in a bowl of ice water to stop the cooking process for approximately 4-5 minutes. Cut kernels off the cob and place in a medium bowl.
Combine corn kernels with red onion, apple cider vinegar, olive oil, and season with salt and pepper. Just before serving, chiffonade the basil leaves: stack basil leaves on top of each other and roll up into a “cigar” shape. Thinly slice basil leaves across the “cigar” into tiny strips. Toss in the chiffonade basil, taste for seasonings and serve.
Can be made a few hours ahead of time without the basil. Add basil just before serving.